[PATCH] mm/THP: Don't use HPAGE_SHIFT in transparent hugepage code

[PATCH] mm/THP: Don't use HPAGE_SHIFT in transparent hugepage code

[Aneesh Kumar K.V]

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

For architectures like powerpc that support multiple explicit hugepage
sizes, HPAGE_SHIFT indicate the default explicit hugepage shift. For
THP to work the hugepage size should be same as PMD_SIZE. So use
PMD_SHIFT directly. So move the define outside CONFIG_TRANSPARENT_HUGEPAGE
#ifdef because we want to use these defines in generic code with
if (pmd_trans_huge()) conditional.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 include/linux/huge_mm.h | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 528454c..cc276d2 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -58,12 +58,11 @@ extern pmd_t *page_check_address_pmd(struct page *page,
 
 #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
 #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
+#define HPAGE_PMD_SHIFT PMD_SHIFT
+#define HPAGE_PMD_SIZE	((1UL) << HPAGE_PMD_SHIFT)
+#define HPAGE_PMD_MASK	(~(HPAGE_PMD_SIZE - 1))
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#define HPAGE_PMD_SHIFT HPAGE_SHIFT
-#define HPAGE_PMD_MASK HPAGE_MASK
-#define HPAGE_PMD_SIZE HPAGE_SIZE
-
 extern bool is_vma_temporary_stack(struct vm_area_struct *vma);
 
 #define transparent_hugepage_enabled(__vma)				\
@@ -181,9 +180,6 @@ extern int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vm
 				unsigned long addr, pmd_t pmd, pmd_t *pmdp);
 
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
-#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
-#define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; })
-#define HPAGE_PMD_SIZE ({ BUILD_BUG(); 0; })
 
 #define hpage_nr_pages(x) 1
 
-- 
1.8.1.2

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Re: [PATCH] mm/THP: Don't use HPAGE_SHIFT in transparent hugepage code

[Kirill A. Shutemov]

On Tue, May 07, 2013 at 02:22:32AM +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> 
> For architectures like powerpc that support multiple explicit hugepage
> sizes, HPAGE_SHIFT indicate the default explicit hugepage shift. For
> THP to work the hugepage size should be same as PMD_SIZE. So use
> PMD_SHIFT directly. So move the define outside CONFIG_TRANSPARENT_HUGEPAGE
> #ifdef because we want to use these defines in generic code with
> if (pmd_trans_huge()) conditional.

Sorry, I haven't got why you move it outside #ifdef.
If CONFIG_TRANSPARENT_HUGEPAGE disabled pmd_trans_huge() will be 0 in
compile time, so BUILD_BUG() will be optimize out by GCC.

The BUILD_BUGs are useful. It's bug if you *really* use the defines with
THP disabled.

-- 
 Kirill A. Shutemov

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Re: [PATCH] mm/THP: Don't use HPAGE_SHIFT in transparent hugepage code

[Kirill A. Shutemov]

On Tue, May 07, 2013 at 02:22:32AM +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> 
> For architectures like powerpc that support multiple explicit hugepage
> sizes, HPAGE_SHIFT indicate the default explicit hugepage shift. For
> THP to work the hugepage size should be same as PMD_SIZE. So use
> PMD_SHIFT directly. So move the define outside CONFIG_TRANSPARENT_HUGEPAGE
> #ifdef because we want to use these defines in generic code with
> if (pmd_trans_huge()) conditional.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
>  include/linux/huge_mm.h | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 528454c..cc276d2 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -58,12 +58,11 @@ extern pmd_t *page_check_address_pmd(struct page *page,
>  
>  #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
>  #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
> +#define HPAGE_PMD_SHIFT PMD_SHIFT

What about:

#ifndef HPAGE_PMD_SHIFT
#define HPAGE_PMD_SHIFT HPAGE_SHIFT
#endif

And define HPAGE_PMD_SHIFT in arch code if HPAGE_SHIFT is not suitable?


> +#define HPAGE_PMD_SIZE	((1UL) << HPAGE_PMD_SHIFT)
> +#define HPAGE_PMD_MASK	(~(HPAGE_PMD_SIZE - 1))
>  
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -#define HPAGE_PMD_SHIFT HPAGE_SHIFT
> -#define HPAGE_PMD_MASK HPAGE_MASK
> -#define HPAGE_PMD_SIZE HPAGE_SIZE
> -
>  extern bool is_vma_temporary_stack(struct vm_area_struct *vma);
>  
>  #define transparent_hugepage_enabled(__vma)				\
> @@ -181,9 +180,6 @@ extern int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vm
>  				unsigned long addr, pmd_t pmd, pmd_t *pmdp);
>  
>  #else /* CONFIG_TRANSPARENT_HUGEPAGE */
> -#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
> -#define HPAGE_PMD_MASK ({ BUILD_BUG(); 0; })
> -#define HPAGE_PMD_SIZE ({ BUILD_BUG(); 0; })
>  
>  #define hpage_nr_pages(x) 1
>  
> -- 
> 1.8.1.2
> 
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-- 
 Kirill A. Shutemov

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Re: [PATCH] mm/THP: Don't use HPAGE_SHIFT in transparent hugepage code

[Aneesh Kumar K.V]

"Kirill A. Shutemov" <kirill@shutemov.name> writes:

> On Tue, May 07, 2013 at 02:22:32AM +0530, Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>> 
>> For architectures like powerpc that support multiple explicit hugepage
>> sizes, HPAGE_SHIFT indicate the default explicit hugepage shift. For
>> THP to work the hugepage size should be same as PMD_SIZE. So use
>> PMD_SHIFT directly. So move the define outside CONFIG_TRANSPARENT_HUGEPAGE
>> #ifdef because we want to use these defines in generic code with
>> if (pmd_trans_huge()) conditional.
>> 
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>> ---
>>  include/linux/huge_mm.h | 10 +++-------
>>  1 file changed, 3 insertions(+), 7 deletions(-)
>> 
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 528454c..cc276d2 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -58,12 +58,11 @@ extern pmd_t *page_check_address_pmd(struct page *page,
>>  
>>  #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
>>  #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
>> +#define HPAGE_PMD_SHIFT PMD_SHIFT
>
> What about:
>
> #ifndef HPAGE_PMD_SHIFT
> #define HPAGE_PMD_SHIFT HPAGE_SHIFT
> #endif
>
> And define HPAGE_PMD_SHIFT in arch code if HPAGE_SHIFT is not
> suitable?


That would work for me provided the BUILD_BUG_ON is also taken care.
But is there a reason why we want to do that ? Will any value other
than PMD_SHIFT work ?

The below patch shows how we want to use these. To avoid those
BUILD_BUG_ON I ended up doing HUGE_PAGE_SIZE and HUGE_PAGE_MASK

https://lists.ozlabs.org/pipermail/linuxppc-dev/2013-April/105631.html

-aneesh

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